Method and apparatus for cell coordination in heterogeneous cellular networks

ABSTRACT

There is provided a method and apparatus for coordinating cells in a heterogeneous network. A serving cell determines scheduling parameters for scheduling a UE intermittently between a serving cell and at least one coordinating cell. The scheduling parameters define a cycle for the UE in which the UE alternates between listening to the serving cell and each of the coordinating cells. Timing offsets between the serving cell and the coordinating cells is determined by a UE and reported back to the eNB of the serving cell.

FIELD OF THE DISCLOSURE

The present disclosure relates to heterogeneous cellular networks and inparticular relates to a method of cell coordination in heterogeneouscellular networks.

BACKGROUND

A clustered cell deployment where a large number of low-power cells(deployed in an unplanned manner) within a macro cell coverage isconsidered. Pico cells and femto or small cell clusters may be situatedwithin the coverage of a macro cell. When a user equipment (‘UE’) movesthrough a path which crosses some of these pico or small cells, it mayundergo many handovers. For example, a UE which traverses between twopico cells will undergo two handovers: one from the first pico cell tothe macro cell, and from the macro cell to the next pico cell.

The above mentioned handovers result in data interruption for eachhandover.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be better understood with reference to thedrawings, in which:

FIG. 1 is a block diagram illustrating one example of a macro cellcomprising pico cells and femto cells;

FIG. 2 is a data flow diagram illustrating current handover procedures;

FIG. 3A is a block diagram illustrating a UE served by a macro cell;

FIG. 3B is a block diagram illustrating a UE receiving control signalingfrom a macro cell but receiving data from a low power cell;

FIG. 3C is a block diagram illustrating a UE served by a low power cell;

FIG. 3D is a block diagram illustrating a UE receiving control signalingfrom a macro cell but receiving data from a low power cell;

FIG. 4 is a data flow diagram illustrating a procedure for data/controloffloading;

FIG. 5 is a diagram illustrating radio resource scheduling for a UEaccording to at least one embodiment of the present disclosure;

FIG. 6 is a data flow diagram illustrating how coordinating cells and aUE are configured according to at least one embodiment of the presentdisclosure;

FIG. 7 is a block diagram illustrating a MAC control element accordingto at least one embodiment of the present disclosure;

FIG. 8 is a data flow diagram illustrating how a serving cell requestsand receives subframe offset information for the coordinating cells froma UE;

FIG. 9 is a block diagram of an example user equipment; and

FIG. 10 is a block diagram showing a simplified example network element.

DETAILED DESCRIPTION

The present disclosure provides a method for radio resource schedulingfor a user equipment (‘UE’) in a heterogeneous network, comprisingreceiving at the UE, scheduling parameters including a first value and asecond value; listening, at the UE, to a serving cell for a number ofconsecutive subframes corresponding with the first value; and listening,at the UE, to at least one coordinating cell for a number of consecutivesubframes corresponding with the second value.

The present disclosure further provides a user equipment (‘UE’),comprising a processor and a communication subsystem; wherein theprocessor and the communication subsystem cooperate to receivescheduling parameters including a first value and a second value; listento a serving cell for a number of consecutive subframes correspondingwith the first value; and listen to at least one coordinating cell for anumber of consecutive subframes corresponding with the second value.

The present disclosure further provides a method for radio resourcescheduling for a user equipment (‘UE’) in a heterogeneous network,comprising sending, from a serving cell, scheduling parameters to theUE, the scheduling parameters indicating subframes associated to theserving cell and subframes associated to a plurality of coordinatingcells; and establishing, at the eNB of the serving cell, a connectionwith the UE during the subframes associated to the serving cell.

The present disclosure further provides an enhanced Node B (‘eNB’) of aserving cell, configured for radio resource scheduling of a userequipment (‘UE’) in a heterogeneous network, comprising a processor anda communication subsystem; wherein the processor and the communicationsubsystem cooperate to send scheduling parameters to the UE, thescheduling parameters indicating subframes associated to the servingcell and subframes associated to a plurality of coordinating cells; andestablish a connection with the UE during the subframes associated tothe serving cell.

The present disclosure further provides a method for synchronizing aserving cell and at least one coordinating cell, comprising sending,from the serving cell, a request to a UE to measure a subframe offsetfor each of the at least one coordinating cell; receiving, at theserving cell, from the UE, the subframe offset for each of the at leastone coordinating cell; and determining, at the serving cell, subframenumbers for each of the at least one coordinating cell based on thesubframe offset for each of the at least one coordinating cell.

The present disclosure further provides an enhanced Node B (‘eNB’) of aserving cell, configured for synchronizing the serving cell and at leastone coordinating cell, comprising a processor and a communicationsubsystem; wherein the processor and the communication subsystemcooperate to send a request to a UE to measure a subframe offset foreach of the at least one coordinating cell; receive from the UE thesubframe offset for each of the at least one coordinating cell; anddetermine subframe numbers for each of the at least one coordinatingcell based on the subframe offset for each of the at least onecoordinating cell.

The present disclosure further provides a method for synchronizing aserving cell and at least one coordinating cell, comprising receiving,at a UE, a request to measure a subframe offset for each of the at leastone coordinating cell; computing, a the UE, the subframe offset for eachof the at least one coordinating cell; and sending, from the UE to theserving cell, the subframe offset for each of the at least onecoordinating cell.

The present disclosure further provides a user equipment (‘UE’)comprising a processor and a communication subsystem; wherein theprocessor and the communication subsystem cooperate to receive a requestto measure a subframe offset for each of the at least one coordinatingcell; compute the subframe offset for each of the at least onecoordinating cell; and send to the serving cell, the subframe offset foreach of the at least one coordinating cell.

Reference is now made to FIG. 1. FIG. 1 illustrates a macro cell 10,served by eNB 20. Macro cell 10 includes pico cells 30 a and 30 b. Asillustrated by arrows, pico cells 30 a and 30 b communicate with thecore network 60 directly, as does macro cell 10. Macro cell 10 furtherincludes femto cells 40 a, 40 b and 40 c, who are connected to the corenetwork 60 via Home eNB Gateway (‘HeNB-GW’) 50.

As seen in FIG. 1, a UE moving in the trajectories indicated by arrows Aor B will undergo many handovers.

Reference is now made to FIG. 2, showing a handover procedure between aserving eNB and a target eNB in a Third Generation Partnership Project(3GPP) Long Term Evolution (LTE) architecture. While the presentdisclosure relates to the 3GPP LTE architecture, the present disclosureis not so limited and concepts described therein are applicable to othertypes of network architecture.

At message 230, the UE 210 sends a measurement report to the serving eNB212. The serving eNB 212 makes a handover decision based on themeasurement report, and in the event the serving eNB 212 decides that ahandover is required, a handover request is sent to target eNB 214, atmessage 232. In response, a handover request ACK is provided to theserving eNB at 234 and the target eNB 214 decides if it has sufficientresources to accept UE 210.

At message 236, the serving eNB 212 transmits an RRC reconfigurationmessage to the UE 210, for assisting the UE in configuring itself forcommunication with the target eNB 214.

At message 238, the serving eNB 212 transmits unacknowledged datapackets intended for UE 210 to target eNB 214.

At message 240, the UE indicates to target eNB 214 that its RRCreconfiguration is complete.

At block 242, path switch messages are exchanged between the target eNB214, the Mobility Management Entity (‘MME’) 216, the Serving Gateway(‘S-GW’) 218, and the serving eNB 212. The path switch procedure informsthe network of the handover.

Once the target eNB 214 receives an acknowledgement of the path switchmessages from MME 216, target eNB 214 sends a UE Context Release messageto the serving eNB 212, indicating that the handover is successfullycompleted.

Importantly, during a successful handover procedure as described above,the UE may not send uplink data during the period indicated by bracket250, and the UE may not receive downlink data during the periodindicated by bracket 260.

Reference is now made to FIGS. 3A, 3B, 3C, and 3D showing a UE atdifferent positions within a macro cell comprising a low power cell.

Low power cells may be stand-alone or non-stand-alone. A stand-alonecell is a cell through which the UE can attach to the LTE network. Anon-stand-alone cell is a cell through which the UE may not attachdirectly to the LTE network. When the low power cell is a stand-alonecell, a UE can perform a cell search and find a cell on a frequency andattach itself to the LTE network by connecting to that cell.

Since the macro cells are typically planned for large coverage areas,generally control messages such as Radio Resource Control (‘RRC’) andNon Access Stratum (‘NAS’) signals are transmitted and received throughthe macro cell. In some cases, the data may be routed through the lowpower cell if there is a dearth of radio resources at the macro cell.

In FIG. 3A, the UE 310 is served by macro cell 312, as it is outside thecoverage area of low power cell 314. Control signaling from MME 316(represented by short-dashed line) is routed to the UE 310 through macrocell 312, as is data from S-GW 318 (represented by long-dashed lines).

In FIG. 3B, UE 320 is within Cell Range Expansion (‘CRE’) region 325 oflow power cell 324. In the scenario of FIG. 3B, the UE is arriving inCRE 325 from the macro cell. As shown in FIG. 3B, data from S-GW isrouted to the macro cell 322, to low power cell 324, and then to the UE320. Control signaling from MME 326 is routed from the macro cell 322directly to the UE 325.

In FIG. 3C, UE 330 is within the coverage area of low power cell 334,and both data from S-GW 338 and control signaling from MME 336 arerouted through low power cell 334 to the UE 330. However, UE 330 couldalso connect to both macro cell 332 and low power cell 334, particularlyif low power cell 334 is a non-stand-alone cell.

In FIG. 3D, UE 340 is within CRE 345 of low power cell 344, as in thecase of FIG. 3B. However, in FIG. 3D, the UE was previously connected tolow power cell 344 and is moving towards macro cell 342. As shown inFIG. 3D, data from S-GW is routed through low power cell 344, andcontrol signaling from MME 346 is routed through low power cell 344, tomacro cell 342, and then to the UE 340.

Therefore, a serving cell may offload data or control signaling to anear-by cell. A procedure for data offloading is shown with reference toFIG. 4. In FIG. 4, a UE 410 communicates with macro eNB 412 and can alsosee low power eNB 414. Both macro eNB 412 and low power eNB 414 cancommunicate with MME 416 and S-GW 418.

As seen in FIG. 4, at message 430 a measurement report is sent from theUE 410 to the macro eNB 412. At block 432, the data offloading procedureis performed. Then, at block 434, data is forwarded between the macroeNB 412 and the low power eNB 414.

At block 436, the UE performs an uplink synchronization with the lowpower eNB 414, and indicates that RRC Reconfiguration is complete atmessage 438. Notably, the path switch procedure 242 shown in FIG. 2 isnot performed.

After the data offloading procedure of FIG. 4, uplink messages travel asillustrated by dashed line 440. Specifically, an uplink message goesfrom UE 410 to low power eNB 414, to macro eNB 412, and to S-GW 418.Similarly, downlink messages go from S-GW 418 to macro eNB 412, to lowpower eNB 414, to UE 410.

In a typical heterogeneous cellular deployment, low-power cells, such aspico cells or femto cells are deployed as an overlay to the existingplanned homogeneous deployments. Normally the overlay deployment is donein an unplanned manner. The overlay deployment is intended to meet thedemand for ever-increasing mobile data applications or to improvecoverage. As seen above, the serving eNB may offload data or controlplane traffic for a UE via a near-by low power cell. During dataoffloading, the UE is in an RRC_connected state with both the servingcell and the coordinating cell, at the same time. Therefore, theresources assigned by each of the serving cell and the coordinatingcells should be coordinated properly to avoid conflicts. Propercoordination may require accurate knowledge of the subframe timingdifferences between the serving eNB and the coordinating eNB.

Furthermore, low power eNBs may be installed independently and poweredon and off as needed.

Resource Allocation Between Macro and Low-Power eNBs

Static Scheduling

According to one embodiment, UEs may be pre-scheduled to listen to theserving cell and the coordinating cell intermittently. FIG. 5illustrates the tuning of a radio on the UE, and in particular, thetuning to the frequency of the macro cell, small cell and transitionperiods. As illustrated in FIG. 5, the UE is scheduled to be incommunication with the macro eNB for N_(M) subframes (or milliseconds)and with the low power cell for N_(L) subframes in every L consecutivesubframes. For every transition from the macro cell to the low powercell and vice versa, N_(R) subframes are allotted to the UE to allow theUE to prepare for the transition. In some implementation, the N_(R)subframes may include a number of extra subframes beyond the subframesneeded for UE transition. During the extra subframes, the UE may listento neither the macro cell nor the low power cell. In at least someembodiments, the UE prepares for the transition by retuning itstransceiver to a different frequency or adjusting its transmissionpower.

In at least some embodiments, the parameters N_(M), N_(L), and N_(R) areexchanged between the serving cell and the coordinating cells before thedata offloading commences. The serving cell, whether it is the macrocell or the low power cell, may decide the bandwidth sharing betweencontrol and data transmissions and set appropriate values for N_(M),N_(L), and N_(R), and inform the coordinating cells and the UE. In atleast some embodiments, initial bandwidth estimates for data offloadingmay be based on quality of service (‘QoS’) requirements of anapplication. Similarly, an estimate of the bandwidth is required for thecontrol signal offloading. In at least some embodiments, the bandwidthsare further adjusted when data transmission commences.

As seen in FIG. 5, the UE may listen to a macro cell or a low power cellintermittently, based on the values of N_(M), N_(L), and N_(R). In FIG.5, a bolded line indicates that the UE listens to the corresponding cellfor the period represented by the length of the line. Thus, at 520 theUE listens to the low power cell. At 530, the UE transitions between thelow power cell and the macro cell, and at 540 the UE listens to themacro cell.

Also as seen in FIG. 5, the UE listens to the low power cell for N_(L)subframes, to the macro cell for N_(M) subframes, and uses N_(R)subframes for transitioning between the low power cell and the macrocell. The length of the cycle is L, such that L=N_(M)+N_(L)+2*N_(R). Insome implementation, the length of the cycle L could be more thanN_(M)+N_(L)+2*N_(R) and the UE listens to neither the macro cell nor thesmall cell during the last L−(N_(M)+N_(L)+2*N_(R)) subframes.

In at least some embodiments, the UE communicates with the macro cellduring subframes n to (n+N_(M)−1), when n satisfies the condition mod(n,L)=p, where p is a number between 0 and L−1.

If the UE starts communicating with the macro cell at subframe n, itwill start transitioning to the macro cell at subframe n−N_(R).

In cases where there are two coordinating cells, the UE will communicatewith the serving cell and first coordinating cell during the subframes(n+N_(R), n+N_(R)+N_(M)−1) and (n+N_(M)+2N_(R), n+N_(M)+2N_(R)+N_(L1)−1)respectively, where n is the subframe at which the UE startstransitioning to the serving cell, and N_(L1) is the number of subframesreserved for listening to the first coordinating cell.

Generally, if there are C coordinating cells, the UE will communicatewith the i-th coordinating cell starting at subframe A and ending atsubframe B, such that:

$\begin{matrix}{A + n + N_{m} + {\left( {i + 1} \right)N_{R}} + {\sum\limits_{j = 1}^{i - 1}N_{Lj}}} & (1)\end{matrix}$

and,

$\begin{matrix}{B = {n + N_{M} + {\left( {i + 1} \right)N_{R}} + {\sum\limits_{j = 1}^{i - 1}N_{Lj}} + N_{Li} - 1.}} & (2)\end{matrix}$

Where N_(LJ) is the number of subframes during which the UE communicateswith the j-th coordinating cell. According to this convention, thelength of the cycle, L is computed by:

$\begin{matrix}{L = {N_{M} + {\left( {C + 1} \right)N_{R}} + {\sum\limits_{j = 1}^{C}N_{Lj}}}} & (3)\end{matrix}$

Reference is now made to FIG. 6. FIG. 6 shows a message flow diagram asshown in FIG. 4 but with additional steps to configure the serving cellsand the low power cells with the coordination parameters. Notably, FIG.6 depicts a scenario in which the macro cell is the serving cell.

The procedure starts with message 630 in which a measurement report issent from the UE 610 to the macro cell 612. At block 632, the dataoffloading procedure is performed, and at block 634 data is forwardedbetween the macro cell and the low power cell or cells.

As shown with message 636, the macro cell 612 sends a CoordinationConfiguration Request message to the low power cell or cells. In atleast one embodiment, the Coordination Configuration Request is includedin an RRC Connection Reconfiguration message. In at least someembodiments, the message includes some or all of the followingparameters:

-   -   the coordination cell list (including Physical Cell Identifier        (‘PCI’) and carrier frequency;    -   the cell association time for each coordinating cell N_(L);    -   serving cell association time N_(M);    -   switching time N_(R);    -   cyclic parameter p.

Using message 638, the low power cell responds with an acknowledgementof the Coordination Configuration Request message. In at least someembodiments, the low power cell's response may include changes to theparameters provided in the Coordination Configuration Request message.If there is more than one low power cell, each low power cell mayprovide proposed changes to the parameters with respect to itself.

In some embodiments, messages 636 and 638 are sent after the uplinksynchronization 640. In other embodiments, messages 636 and 638 can besent as part of Data Offloading Procedure 632. For example, coordinationconfiguration messages may be piggybacked onto a handover request and ahandover request acknowledgement. One example of the coordinationconfiguration message is shown in Table 1.

TABLE 1 Coordination Configuration Message IE/Group IE type andSemantics Assigned Name Presence Range reference description CriticalityCriticality Message M 9.2.13 Yes reject Type Serving eNB M eNB UEAllocated at Yes reject UE X2AP ID X2AP ID the source 9.2.24 eNB Cause M9.2.6a Yes ignore Coordinating M eNB UE Allocated at Yes reject eNB UEX2AP ID the X2AP ID 9.2.24 coordinating eNB UE Context 1 Yes rejectInformation >Association M OCTET Includes the — — Context STRING RRCmessage with the UE association information

An example of the coordination configuration message response is shownin Table 2.

TABLE 2 Coordination Configuration Message Response IE type IE/Group andSemantics Assigned Name Presence Range reference description CriticalityCriticality Message M 9.2.13 Yes reject Type Coordinating M eNB UEAllocated at Yes reject eNB UE X2AP ID the X2AP ID 9.2.24 coordinatingeNB Cause M 9.2.6a Yes ignore Serving eNB M eNB UE Allocated at Yesreject UE X2AP ID X2AP ID the source 9.2.24 eNB UE Context 1 — ignoreInformation >Association M OCTET Includes the — — Context STRING RRCmessage with the UE association information with suggested changes.

After the UL synchronization 640, the serving cell 612 transmits thecoordination parameters to the UE 610 with message 644.

Optionally, the coordination parameters are also provided to the UE byeach of the low power cells 614 with message 646.

By multicasting the coordination parameters from multiple cells, theprobability of correct detection at the UE can be increased. Furtherimprovements in reception can be achieved if the identical messagestransmitted by all the coordinating cells can be soft combined by the UEduring the reception. However, the UE should know the transmissiontiming of these messages from each of the coordinating cells.

The value of L, the length of a full cycle in which the UE listens tothe serving cell and each of the coordinating cells, can be networkspecific, or can be cell specific. When L is configured as a cellspecific parameter, its value may be broadcast by the serving cell. Forexample, such broadcast may be in System Information Block Type 2(‘SIB2’) as shown below with regards to Table 3.

TABLE 3 SystemInformationBlockType2 information element -- ASN1STARTSystemInformationBlockType2 ::=  SEQUENCE {  ac-BarringInfo SEQUENCE {  ac-BarringForEmergency   BOOLEAN,   ac-BarringForMO-Signalling  AC-BarringConfig  OPTIONAL, -- Need OP   ac-BarringForMO-Data  AC-BarringConfig OPTIONAL -  }  OPTIONAL, -- Need OP radioResourceConfigCommon  RadioResourceConfigCommonSIB, ue-TimersAndConstants  UE-TimersAndConstants,  freqInfo SEQUENCE {  ul-CarrierFreq  ARFCN-ValueEUTRA  OPTIONAL, -- Need OP   ul-Bandwidth ENUMERATED {n6, n15, n25, n50, n75, n100}  OPTIONAL, -- Need OP  additionalSpectrumEmission   AdditionalSpectrumEmission  }, mbsfn-SubframeConfigList MBSFN-SubframeConfigList  OPTIONAL, -- Need OR timeAlignmentTimerCommon  TimeAlignmentTimer,  ..., lateNonCriticalExtension OCTET STRING  OPTIONAL, -- Need OP [[ ssac-Barring ForMMTEL-Voice-r9 AC-BarringConfig  OPTIONAL, -- NeedOP     ssac-Barring ForMMTEL-Video-r9 AC-BarringConfig  OPTIONAL-- NeedOP  ]],  [[ ac-BarringForCSFB-r10 AC-BarringConfig OPTIONAL -  ]], [[ UEAssociationConfig-rxxxx UEAssociationConfig  OPTIONAL-- Need OP ]] } AC-BarringConfig ::= SEQUENCE {  ac-BarringFactor  ENUMERATED {  p00, p05, p10, p15, p20, p25, p30, p40,   p50, p60, p70, p75, p80,p85, p90, p95},  ac-BarringTime  ENUMERATED {s4, s8, s16, s32, s64,s128, s256, s512},  ac-BarringForSpecialAC   BIT STRING (SIZE(5)) }UEAssociationConfig-rxxxx ::=    SEQUENCE {  L-typical N_R-inter-frequency  N_R-intra-frequency  N_L-typical }MBSFN-SubframeConfigList ::=  SEQUENCE (SIZE (1..maxMBSFN- Allocations))OF MBSFN-SubframeConfig -- ASN1STOP

Typical values for L, N_(L), N_(R) for intra and inter-frequency mayalso be provided with SIB2. When the serving cell intends to changethese values or make these values UE-specific, the new parameter valuesor the UE-specific values may be included within an information elementof an RRC message. For example, a UEAssociationInfo information element,as shown in Table 4 below, may be used. According to some embodiments,if the UE receives different parameter values in SIB2 and theUEAssociationInfo information element, the UE may use the parametersfrom the UEAssociationInfo information element. In another alternative,the values for L, N_(L), N_(R) may also be provided in other SIBsignaling or other broadcast messages.

TABLE 4 UEAssociationInfo information element -- ASN1STARTUEAssociationInfo ::= SEQUENCE {   coordinatingCellList    CoordinatingCellList    OPTIONAL,  -- Need OR   N_M        ENUMERATED{ },   N_R         ENUMERATED{ }   OPTIONAL,  -- NeedOP   p       ENUMERATED{ }   ... } CoordinatingCellList ::= SEQUENCE(SIZE (1..maxCellIntra)) OF IntraFreqNeighCellInfoIntraFreqNeighCellInfo ::= SEQUENCE {   physCellId         PhysCellId,  carrierFrequency         CarrierFrequency,   N_L           ENUMERATED{} } -- ASN1STOP

The serving cell may optimize L such that there is no conflict betweenthe DRX cycle and the resource sharing cycle. Alternatively, the servingcell and the coordinating cells should be aware of both these cycles sothat there is no conflict.

Dynamic Scheduling

As presented above, static resource partitioning for control signalingand data may be effective. However, based on the value of L, datatransmission interruptions or loss of data may be more or less frequent.For example, while the UE is communicating with a low power cell, the UEmay be required to send a measurement report to the macro cell. In orderto send the measurement report, the UE must wait until the nextopportunity to communicate with the macro cell, causing a delay in themeasurement report reporting. This problem can be partially alleviatedby selecting a small value of L. However, a small value of L may reducethe system and spectrum usage efficiency, η, defined in equation 4below.

$\begin{matrix}{\eta = \frac{N_{R}}{L}} & (4)\end{matrix}$

To improve the spectrum usage efficiency, resource sharing can be fullyor partially dynamic. For example, a large value for L can be configuredand if there is a need for RRC or NAS signaling, a low power cell maydirect the UE to listen to the macro cell for RRC messages. Similarly,on the uplink, the UE may indicate to the low power cell a need forcommunications with the macro cell during a data transmission.

During downlink communications, the need for sending an RRC message toan RRC_connected UE is decided either by the macro cell or the low powercell, depending on how the RRC functionality is split between the macrocell and the low power cells. If a low power cell makes a decision tosend an RRC message and the UE is associated with the low power cell atthat time and for the next ζ subframes, the low power cell can include aMedium Access Control (‘MAC’) element to indicate that the UE shouldlisten to the macro cell after β subframes, where ζ>β+T, and Trepresents the expected delay incurred by coordination signaling over abackhaul link between eNBs.

On the other hand, if the macro cell makes the decision to send an RRCmessage, the macro cell may inform the low power cell to inform the UEof its decision.

On the uplink, if the UE intends to send an RRC or NAS message, the UEmay indicate its intentions on the Physical Uplink Shared Channel(‘PUSCH’) on a MAC control element. In another alternative, a new layer1 control signaling may be designed for this purpose, or the currentscheduling request (SR) channel may be extended to achieve this, by forexample, providing another SR channel but with lower rate. Butgenerally, for the simplicity, MAC control element alternative isslightly preferred.

Specifically, one of the reserved values for the Logical ChannelIdentifier (‘LCID’) of a MAC Control Element may be used to indicate arequest for an RRC message to a coordinating cell, or an indication thatan RRC message was scheduled by a coordinating cell, as shown in bold inTables 5 and 6 below. While Tables 5 and 6 indicate the value ‘01011’,those skilled in the art will appreciate that any of the reserved valuesmay be used for this purpose.

TABLE 5 Values of LCID for Downlink MAC CE Index LCID values 00000 CCCH00001-01010 Identity of the logical channel 01011 Indication of RRCmessage scheduled by a coordinating cell 01100-11010 Reserved 11011Activation/Deactivation 11100 UE Contention Resolution Identity 11101Timing Advance Command 11110 DRX Command 11111 Padding

TABLE 6 Values of LCID for Uplink MAC CE Index LCID values 00000 CCCH00001-01010 Identity of the logical channel 01011 Grant Request for RRCmessage to a coordinating cell 01100-11000 Reserved 11001 Extended PowerHeadroom Report 11010 Power Headroom Report 11011 C-RNTI 11100 TruncatedBSR 11101 Short BSR 11110 Long BSR 11111 Padding

The MAC control element is identified by a MAC PDU subheader with theLCID field as specified in Tables 5 and 6 above.

An example of a MAC control element is shown with respect to FIG. 7. Asseen in FIG. 7, the MAC control element includes a first portion (notshown) represented at 710. The MAC control element further includes avalue 720 for β, a value 730 for β1, and a value 740 for the CellID.

The MAC control element has a fixed size and comprises the followingfields:

-   -   β: This field contains the subframe offset. The length of the        field is 8 bits.    -   β1: This field contains the subframe range. The length of this        field is 8 bits.    -   CellID: This field contains the coordinating cell ID. The cell        ID may be a temporary ID assigned by the serving cell during the        coordination configuration.

In some embodiments, the UE receives the RRC or NAS message betweensubframe (n+β) and subframe (n+β+β1), where n is the current subframenumber.

UE Assisted Subframe-Number-Offset Determination

As outlined above, when the UE is initially attached to the macro celland moving towards a low power cell, the data traffic may be offloadedby the macro cell to the low power cell. During the initiation of thisoffloading procedure, the macro eNB should configure the coordinationparameters and inform the UE of these parameters. These parameters mayinclude pre-scheduling information, so that the UE may be aware of thetime during which it has the opportunity to communicate with the macrocell or the MME.

For example, the UE may be configured to listen to the macro cell if thesubframe number n meets the following criterion: mod(n, L)=p; where n isthe macro cell's subframe number. L and p are communicated to the UE bythe macro cell during the coordination configuration setup, as is thevalue of N_(R). These values are also communicated to the low powercells over the backhaul interface. Low power cells may schedule datapackets for the UE during the subframes assigned to them as described inFIG. 5. Low power cells should be aware of the relative subframenumbering of the macro cell to schedule transmission of data packets.However, subframe numbers between two eNBs may not be synchronized. Ifthe eNBs try to synchronize their subframe numbers by exchanginginformation over the backhaul interface, the unpredictability of thebackhaul delay means that synchronization may fail.

This issue may be resolved by involving the UE. For example, the UE maybe asked by the serving cell to read the system frame number (SFN) andthe subframe number of coordinating cells, and the difference may bereported to the serving cell.

Normally, this measurement may take some time if the UE is not alreadysynchronized with the coordinating cells. The serving cell may provide afixed time for uplink resources in which the UE may send the SFN deltareport.

In at least some embodiments, the SFN delta report is sent as an RRCmessage or in a MAC payload.

In at least some embodiments, the UE computes the subframe number deltafor a coordinating cell as follows.

The UE obtains the radio frame number for the serving cell, n_(R) andthe subframe number within the radio frame, n_(s). Similarly, the UEobtains the radio frame number for the coordinating cell m_(R), and thesubframe number within the radio frame, m_(s).

The subframe number for the serving cell is computed as n=10n_(r)+n_(s).and the subframe number for the coordinating cell is computed as m=10m_(r)+m_(s), assuming there are 10 subframes per radio frame.Accordingly, values n and m represent the subframe number independentlyof a radio frame.

The delta value is then computed as the cyclic difference of values nand m, wherein the cyclic difference is defined by the function f of(n−m) and K, as follows:

$\begin{matrix}\begin{matrix}{{f\left( {{n - m},K} \right)} = {n - m}} & {{{if}\mspace{14mu} - \frac{K}{2}} \leq \left( {n - m} \right) < \frac{K}{2}} \\{{f\left( {{n - m},K} \right)} = {n - m + K}} & {{{if} - K} < \left( {n - m} \right) < \frac{- K}{2}} \\{{f\left( {{n - m},k} \right)} = {n - m - K}} & {{{if}\mspace{14mu} \frac{K}{2}} \leq \left( {n - m} \right) < K}\end{matrix} & (5)\end{matrix}$

In at least some embodiments, the delta value is computed as:

Δ=mod(|n−m|,K)  (6)

In some embodiments, the value of K is 10240 (10 subframes for 1024radio frames), however other values for K may be configured and thepresent disclosure is not so limited.

Alternatively, the differences in SFN and subframe number within a radioframe may be reported separately. The difference in SFN is provided asΔ₁=f (n_(r)−m_(r), 1024) where f is as defined above, and n_(r), andm_(r) are the SFN numbers of the serving cell and the coordinating cell.In at least one embodiment, Δ₁ is represented by 10 bits, including onebit to indicate whether the difference is an advance or a delay.

The difference in subframe number within the radio frame is provided asΔ₂=f(n_(s)−m_(s), 10), where f is as defined above, and n_(s) and m_(s)are the subframe numbers within the radio frame of the serving cell andthe coordinating cell. In at least one embodiment, Δ₂ is represented by4 bits, including one bit to indicate whether the difference is anadvance or a delay.

Since these subframe numbers are static, the serving cell may requestthis measurement from some of the UEs in the RRC_connected state, afirst time when the eNB is powered on, and whenever the eNB or acoordinating cell's eNB configuration is updated.

Alternatively, the serving cell may request the UE and/or thecoordinating cells to measure the relative subframe offset by listeningto an uplink transmission from some of the UEs connected to the servingcell. For example, coordinating cells may listen to an ULsynchronization sequence, such as SRS, to measure the relative subframeoffset. UE specific SRS configuration may be sent to the surroundingcells. The neighboring cells may measure the timing of these transmittedsequences relative to their own uplink timing.

The value of L may be determined by the serving cell. L may be networkspecific or UE specific.

Reference is now made to FIG. 8 which shows the data flow for a servingcell (in this case macro cell 812) requesting subframe offsets from a UE810. A coordinating cell (in this case low power eNB 814) can furthercommunicate with UE 810 and macro eNB 812.

The process starts with message 830, where the UE 810 sends ameasurement report to the macro (or serving) cell 812. After receivingthe measurement report from the UE 810, the macro cell 812 may send aTime Difference (‘TD’) Report Request with message 832 to the UE 810.

The TD Report Request message may include the Cell IDs of cells withrespect to which the serving cell wishes to know the subframe offset.Based on the measurement report, the macro cell 812 would know whichcells the UE is close to, and may select from these cells a subset forwhich the UE may determine the subframe offset.

If the macro cell 812 receives measurement reports from multiple UEs,the macro cell 812 may select a UE that is closest to the cell or cellsthat need to be measured. This may help ensure that the subframe offsetwill be measured with low latency and high accuracy.

Upon receiving the TD Report Request message, the UE may performsubframe number offset determination at block 834 with respect to thecells identified in the message. The macro (or serving) cell 812 shouldthen allow the UE enough time to access downlink message from theidentified cells. For example, if the macro cell and the low power cellsare on different frequencies, the macro cell 812 may give the UE 810 a40 milliseconds gap for receiving 4 consecutive Physical BroadcastChannel (‘PBCH’) transmissions to determine the 2 least significant bitsof the SFN, in one approach. In other cases, for example if the UE isclose to the cell that needs to be measured and the Signal toInterference Noise Ratio (‘SNIR’) is sufficient, a 10 milliseconds gapmay be enough. In some approaches, the macro cell 812 may also providean uplink grant in advance for the UE to send the report.

Using message 836, the UE 810 responds to the macro cell 812 with the TDReport. In at least one embodiment, the TD Report is provided in an RRCmessage. In at least one embodiment, the UE includes a confidencemeasure in the TD Report. The confidence measure indicates the accuracyof the measurement (i.e., an estimate of the measurement error) whichdepends on factors such as the measurement time, the measurementalgorithm, and the like.

UE 810 may obtain the subframe number of the coordinating cell with thecoordinating cell's PCI. First, the UE tries to acquire the subframesynchronization by correlating samples of a received signal with alocally generated Cell-specific Reference Signal (‘CRS’) sequence. TheCRS sequence is generated based on the PCI and a selected slot numberwithin a radio frame and a selected Orthogonal Frequency DivisionMultiplexing (‘OFDM’) symbol number within the slot. Then, the UE readsthe Master Information Block (‘MIB’) transmitted by the cell.

After the TD Report is transmitted by the UE 810, the macro cell 812optionally responds with an ACK with message 838. The above dataoffloading procedure may then be performed, as shown at block 840.

The above procedure for measuring the subframe offset number ofcoordinating cells may be performed after receiving the measurementreport from a UE, as depicted in FIG. 8. Alternatively, the aboveprocedure may be triggered across the network, e.g., by a newlyinstalled eNB, when a eNB is powered on or reset, when a neighboring eNBis reset, or when a eNB receives a message to the effect that a eNB wasturned on.

In at least some embodiments, the TD Report Request, the TD Report andthe TD Report ACK are new messages. In at least some other embodiments,the TD Report Request may be provided over a MAC control element.

The above may be implemented by changing section 5.5.3.1 of the 3GPPTechnical Specification (TS) 36.331 V10.3.0 (2011-09) “TechnicalSpecification: Evolved Universal Terrestrial Radio Access (E-UTRA);Radio Resource Control (RRC); Protocol Specification (Release 10)”incorporated herein by reference, as shown by the bold portions in theexample of Table 7. Further, changes may be made to information elementsto convey the information. For example, the ReportConfigEUTRAinformation element may be amended, as shown by the bold portions inTable 8. Other or different changes are possible.

TABLE 7 Performance Measurement Changes 5.5.3 Performing measurements5.5.3.1 General For all measurements the UE applies the layer 3filtering as specified in 5.5.3.2, before using the measured results forevaluation of reporting criteria or for measurement reporting. The UEshall:  1> whenever the UE has a measConfig, perform RSRP and RSRQmeasurements for    each serving cell, applying for the Pcell the timedomain measurement resource    restriction in accordance withmeasSubframePatternPCell, if configured;  1> for each measId included inthe measIdList within VarMeasConfig:    2> if the purpose for theassociated reportConfig is set to reportCGI:      ... ... ...    2> else   3> if a measurement gap configuration is setup, or    3> if the UEdoes not require measurement gaps to perform the concerned measurements:      4> if s-Measure is not configured; or       4> if s-Measure isconfigured and the Pcell RSRP, after layer 3 filtering, is lower thanthis value:        5> perform the corresponding measurements ofneighbouring cells on the frequencies and RATs indicated in theconcerned measObject, applying for neighboring cells on the primaryfrequency the time domain measurement resource restriction in accordancewith measSubframePatternConfigNeigh, if configured in the concernedmeasObject;       4> if the ue-RxTxTimeDiffPeriodical is configured inthe associated reportConfig:        5> perform the UE Rx-Tx timedifference measurements on the Pcell;       4> if theue-RxTimeDiff-CoordinatingCell is configured in the associatedreportConfig:        5> perform the UE Rx time difference measurementson the Serving Pcell and the coordinating cell;    2> perform theevaluation of reporting criteria as specified in 5.5.4 NOTE 3: Thes-Measure defines when the UE is required to perform measurements. TheUE is however allowed to perform measurements also when the Pcell RSRPexceeds s-Measure, e.g., to measure cells broadcasting a CSG identityfollowing use of the autonomous search function as defined in TS36.304[4]

TABLE 8 ReportConfigEUTRA information element -- ASN1STARTReportConfigEUTRA ::=  SEQUENCE {  triggerType CHOICE {   event SEQUENCE{    eventId  CHOICE {     eventA1   SEQUENCE {      a1-Threshold   ThresholdEUTRA     },     eventA2   SEQUENCE {      a2-Threshold   ThresholdEUTRA    },    eventA3   SEQUENCE {      a3-Offset   INTEGER(−30..30),      reportOnLeave    BOOLEAN     },     eventA4   SEQUENCE {     a4-Threshold    ThresholdEUTRA     },     eventA5   SEQUENCE {     a5-Threshold1    ThresholdEUTRA,      a5-Threshold2   ThresholdEUTRA     },     ...,     eventA6-r10    SEQUENCE {     a6-Offset-r10    INTEGER (−30..30),      a6-ReportLeave-r10 BOOLEAN    },    },    hysteresis   Hysteresis,    timeToTrigger  TimeToTrigger   },   periodical   SEQUENCE {    purpose    ENUMERATED{   reportStrongestCells, reportCGI}   }  },  triggerQuantity ENUMERATED {rsrp, rsrq}  reportQuantity  ENUMERATED{sameAsTriggerQuantity, both},  maxReportCells   INTEGER(1..maxCellReport),  reportInterval  ReportInterval,  reportAmountENUMERATED {r1, r2, r4, r8, r16, r32, r64, infinity},  ...,  [[si-RequestForHO-r9   ENUMERATED {setup} OPTIONAL,-- Cond reportCGI  ue-RxTxTimeDiffPeriodical-r9  ENUMERATED {setup} OPTIONAL -- Need OR ]],  [[ includeLocationInfo-r10  ENUMERATED {true} OPTIONAL, -- CondreportMDT   reportAddNeighMeas-r10 ENUMERATED {setup} OPTIONAL -- NeedOR  ]]  [[ RequestForSubFrameNoDiff-rxx ENUMERATED OPTIONAL,  ue-RxTimeDiff -rxx   ENUMERATED OPTIONAL  ]] } TresholdEUTRA ::=  CHOICE{  threshold-RSRP RSRP-Range,  threshold-RSRQ RSRQ-Range }

The above may be implemented by any UE. One exemplary device isdescribed below with regard to FIG. 9.

UE 900 is typically a two-way wireless communication device having voiceand data communication capabilities. Depending on the exactfunctionality provided, the UE may be referred to as a data messagingdevice, a two-way pager, a wireless e-mail device, a cellular telephonewith data messaging capabilities, a wireless Internet appliance, awireless device, a mobile device, or a data communication device, asexamples.

Where UE 900 is enabled for two-way communication, it may incorporate acommunication subsystem 911, including both a receiver 912 and atransmitter 914, as well as associated components such as one or moreantenna elements 916 and 918, local oscillators (LOs) 913, and aprocessing module such as a digital signal processor (DSP) 920. As willbe apparent to those skilled in the field of communications, theparticular design of the communication subsystem 911 will be dependentupon the communication network in which the device is intended tooperate. The radio frequency front end of communication subsystem 911can be any of the embodiments described above.

Network access requirements will also vary depending upon the type ofnetwork 919. In some networks network access is associated with asubscriber or user of UE 900. A UE may require a removable user identitymodule (RUIM) or a subscriber identity module (SIM) card in order tooperate on a network. The SIM/RUIM interface 944 is normally similar toa card-slot into which a SIM/RUIM card can be inserted and ejected. TheSIM/RUIM card can have memory and hold many key configurations 951, andother information 953 such as identification, and subscriber relatedinformation.

When required network registration or activation procedures have beencompleted, UE 900 may send and receive communication signals over thenetwork 919. As illustrated in FIG. 9, network 919 can consist ofmultiple base stations communicating with the UE.

Signals received by antenna 916 through communication network 919 areinput to receiver 912, which may perform such common receiver functionsas signal amplification, frequency down conversion, filtering, channelselection and the like. A/D conversion of a received signal allows morecomplex communication functions such as demodulation and decoding to beperformed in the DSP 920. In a similar manner, signals to be transmittedare processed, including modulation and encoding for example, by DSP 920and input to transmitter 914 for digital to analog conversion, frequencyup conversion, filtering, amplification and transmission over thecommunication network 919 via antenna 918. DSP 920 not only processescommunication signals, but also provides for receiver and transmittercontrol. For example, the gains applied to communication signals inreceiver 912 and transmitter 914 may be adaptively controlled throughautomatic gain control algorithms implemented in DSP 920.

UE 900 generally includes a processor 938 which controls the overalloperation of the device. Communication functions, including data andvoice communications, are performed through communication subsystem 911.Processor 938 also interacts with further device subsystems such as thedisplay 922, flash memory 924, random access memory (RAM) 926, auxiliaryinput/output (I/O) subsystems 928, serial port 930, one or morekeyboards or keypads 932, speaker 934, microphone 936, othercommunication subsystem 940 such as a short-range communicationssubsystem and any other device subsystems generally designated as 942.Serial port 930 could include a USB port or other port known to those inthe art.

Some of the subsystems shown in FIG. 9 perform communication-relatedfunctions, whereas other subsystems may provide “resident” or on-devicefunctions. Notably, some subsystems, such as keyboard 932 and display922, for example, may be used for both communication-related functions,such as entering a text message for transmission over a communicationnetwork, and device-resident functions such as a calculator or tasklist.

Operating system software used by the processor 938 may be stored in apersistent store such as flash memory 924, which may instead be aread-only memory (ROM) or similar storage element (not shown). Thoseskilled in the art will appreciate that the operating system, specificdevice applications, or parts thereof, may be temporarily loaded into avolatile memory such as RAM 926. Received communication signals may alsobe stored in RAM 926.

As shown, flash memory 924 can be segregated into different areas forboth computer programs 958 and program data storage 950, 952, 954 and956. These different storage types indicate that each program canallocate a portion of flash memory 924 for their own data storagerequirements. Processor 938, in addition to its operating systemfunctions, may enable execution of software applications on the UE. Apredetermined set of applications that control basic operations,including at least data and voice communication applications forexample, will normally be installed on UE 900 during manufacturing.Other applications could be installed subsequently or dynamically.

Applications and software may be stored on any computer readable storagemedium. The computer readable storage medium may be a tangible or intransitory/non-transitory medium such as optical (e.g., CD, DVD, etc.),magnetic (e.g., tape) or other memory known in the art.

One software application may be a personal information manager (PIM)application having the ability to organize and manage data itemsrelating to the user of the UE such as, but not limited to, e-mail,calendar events, voice mails, appointments, and task items. Naturally,one or more memory stores would be available on the UE to facilitatestorage of PIM data items. Such PIM application may have the ability tosend and receive data items, via the wireless network 919. Furtherapplications may also be loaded onto the UE 900 through the network 919,an auxiliary I/O subsystem 928, serial port 930, short-rangecommunications subsystem 940 or any other suitable subsystem 942, andinstalled by a user in the RAM 926 or a non-volatile store (not shown)for execution by the processor 938. Such flexibility in applicationinstallation increases the functionality of the device and may provideenhanced on-device functions, communication-related functions, or both.For example, secure communication applications may enable electroniccommerce functions and other such financial transactions to be performedusing the UE 900.

In a data communication mode, a received signal such as a text messageor web page download will be processed by the communication subsystem911 and input to the processor 938, which may further process thereceived signal for output to the display 922, or alternatively to anauxiliary I/O device 928.

A user of UE 900 may also compose data items such as email messages forexample, using the keyboard 932, which may be a complete alphanumerickeyboard or telephone-type keypad, among others, in conjunction with thedisplay 922 and possibly an auxiliary I/O device 928. Such composeditems may then be transmitted over a communication network through thecommunication subsystem 911.

For voice communications, overall operation of UE 900 is similar, exceptthat received signals would typically be output to a speaker 934 andsignals for transmission would be generated by a microphone 936.Alternative voice or audio I/O subsystems, such as a voice messagerecording subsystem, may also be implemented on UE 900. Although voiceor audio signal output is generally accomplished primarily through thespeaker 934, display 922 may also be used to provide an indication ofthe identity of a calling party, the duration of a voice call, or othervoice call related information for example.

Serial port 930 in FIG. 9 would normally be implemented in a personaldigital assistant (PDA)-type UE for which synchronization with a user'sdesktop computer (not shown) may be desirable, but is an optional devicecomponent. Such a port 930 would enable a user to set preferencesthrough an external device or software application and would extend thecapabilities of UE 900 by providing for information or softwaredownloads to UE 900 other than through a wireless communication network.The alternate download path may for example be used to load anencryption key onto the device through a direct and thus reliable andtrusted connection to thereby enable secure device communication. Aswill be appreciated by those skilled in the art, serial port 930 canfurther be used to connect the UE to a computer to act as a modem.

Other communications subsystems 940, such as a short-rangecommunications subsystem, is a further optional component which mayprovide for communication between UE 900 and different systems ordevices, which need not necessarily be similar devices. For example, thesubsystem 940 may include an infrared device and associated circuits andcomponents or a Bluetooth™ communication module to provide forcommunication with similarly enabled systems and devices. Subsystem 940may further include non-cellular communications such as WiFi or WiMAX.

The above may be implemented by any network element. A simplifiednetwork element is shown with regard to FIG. 10. The network element ofFIG. 10 shows an architecture which may, for example, be used for thebase stations or eNBs described in the embodiments of FIGS. 1 to 8.

In FIG. 10, network element 1010 includes a processor 1020 and acommunications subsystem 1030, where the processor 1020 andcommunications subsystem 1030 cooperate to perform the methods of theembodiments described above.

Processor 1020 is configured to execute programmable logic, which may bestored, along with data, on network element 1010, and shown in theexample of FIG. 10 as memory 1040. Memory 1040 can be any tangiblestorage medium.

Alternatively, or in addition to memory 1040, network element 1010 mayaccess data or programmable logic from an external storage medium, forexample through communications subsystem 1030.

Communications subsystem 1030 allows network element 1010 to communicatewith other network elements.

Communications between the various elements of network element 1010 maybe through an internal bus 1050 in one embodiment. However, other formsof communication are possible.

The embodiments described herein are examples of structures, systems ormethods having elements corresponding to elements of the techniques ofthis application. This written description may enable those skilled inthe art to make and use embodiments having alternative elements thatlikewise correspond to the elements of the techniques of thisapplication. The intended scope of the techniques of this applicationthus includes other structures, systems or methods that do not differfrom the techniques of this application as described herein, and furtherincludes other structures, systems or methods with insubstantialdifferences from the techniques of this application as described herein.

1. A method for radio resource scheduling for a user equipment (‘UE’) in a heterogeneous network, comprising: receiving at the UE, scheduling parameters including a first value and a second value; listening, at the UE, to a serving cell for a number of consecutive subframes corresponding with the first value; and listening, at the UE, to at least one coordinating cell for a number of consecutive subframes corresponding with the second value.
 2. The method of claim 1, further comprising receiving a third value, wherein the UE has a number of subframes corresponding with the third value to transition between the serving cell and the coordinating cell.
 3. The method of claim 1, further comprising listening, at the UE, to at least one of the coordinating cells for a number of consecutive subframes corresponding to the second value.
 4. The method of claim 2 wherein transitioning between the serving cell and the coordinating cells comprises tuning a transceiver of the UE and adjusting transmission power of the UE.
 5. The method of claim 2, wherein the scheduling parameters further include value p, the first value is designated as ‘M’, the second value is designated as ‘L’, the third value is designated as ‘R’, and wherein the UE starts listening to the serving cell at a subframe n, such that mod(n, M+L+2R)=p.
 6. The method of claim 1 wherein the scheduling parameters further include a coordinating cell list, the coordinating cell list comprising at least one of a Physical Cell Identifier (‘PCI’) and carrier frequency for each coordinating cell.
 7. The method of claim 1, wherein the scheduling parameters are received from the serving cell.
 8. The method of claim 7, wherein the scheduling parameters are further received from the plurality of coordinating cells.
 9. The method of claim 1, further comprising: receiving at the UE, during the subframes associated to a first cell, an indication to listen to a second cell; listening to the second cell based on the indication.
 10. The method of claim 9 wherein the first cell is the serving cell and the second cell is one of the coordinating cells.
 11. The method of claim 9 wherein the first cell is one of the coordinating cells and the second cell is the serving cell.
 12. The method of claim 9 wherein the first cell is one of the coordinating cells and the second cell is another of the coordinating cells.
 13. The method of claim 9, wherein the indication is provided in a Medium Access Control (‘MAC’) Control Element.
 14. The method of claim 9, wherein the indication comprises a value β and wherein the UE starts listening to the second cell after β subframes.
 15. The method of claim 14, wherein the indication further comprises a value β1 and wherein the UE listens to the second cell for β1 subframes.
 16. The method of claim 1, further comprising: sending from the UE, while listening to a first cell, a request to send an uplink message to a second cell.
 17. The method of claim 16 wherein the first cell is the serving cell and the second cell is one of the coordinating cells.
 18. The method of claim 16 wherein the first cell is one of the coordinating cells and the second cell is the serving cell.
 19. The method of claim 16 wherein the first cell is one of the coordinating cells and the second cell is another of the coordinating cells.
 20. The method of claim 16, wherein the request is provided in a MAC Control Element. 21.-137. (canceled) 